- Javier Hernandez is only the third player to score at three different World Cups for Mexico (2010, 2014 and 2018) after Cuauhtemoc Blanco (1998, 2002 and 2010) and Rafael Marquez (2006, 2010 and 2014). "It was just noise".
Mexico were awarded a penalty when Jang Hyun-soo handled a cross from Andres Guardado after 23 minutes.
Conditioned by the dry heat that has been a feature of every game at the Rostov Arena, Mexico did not quite have the same thrust and energy as against Germany although they still controlled most of the play and looked far more unsafe.
It's the 50th career worldwide goal for Hernandez, known as "Chicharito".
Only a Germany win will prevent South Korea being knocked out with a group game remaining.
Hernandez added the second in the 66th, scoring his 50th goal for Mexico.
"We have beaten two brilliant and complicated teams, Germany and South Korea", Hernandez said.More news: Days After Buying Time Warner, AT&T Launches New TV Service
Mexico will qualify for the last 16 if they win and Germany fail to beat Sweden. "We've received a lot of praise, we the team, and we've tried to remain focused".
Son Heung-Min gave South Korea fleeting hopes of earning a point with a sublime, curling strike from 25 yards.
The South Koreans, who have lost their opening two matches, kept Ochoa under pressure throughout the match with Son often out-sprinting the Mexican defense.
Mexico relied on keeping possession and long-range shots, with a powerful attempt from Andreas Guardado forcing an athletic save from Jo in the second half.
Vela nearly turned provider two minutes later with a neat ball into Layun, but the former Watford man lashed his effort over from close range.
Mexico will now have its eyes on Sweden and Germany.
South Korea wanted a penalty of their own after the restart when Moon Seon-min's strike clipped Carlos Salcedo's arm, but the referee correctly waved away their appeals.